FIG. 1 is a schematic diagram of an overall architecture of an LTE (Long Term Evolution) system in the related art. As shown in FIG. 1, a LTE architecture comprises an MME (Mobility Management Entity), an SGW (Serving Gateway), a User Equipment or Terminal (called as UE for short) and base stations (eNodeB, called as eNB for short), herein interfaces between the UE and the eNB are Uu interfaces, an interface between the eNB and the MME is an S1-MME (S1 for the control plane) interface, an interface between the eNB and the SGW is an S1-U interface, and interfaces between the eNBs are X2-U (X2-User plane) and X2-C (X2-Control plane) interfaces. In LTE, a protocol stack of the S1-MME interface is divided into the following protocol layers from bottom to top: L1 protocol, L2 protocol, IP (Internet Protocol), SCTP (Stream Control Transmission Protocol), and S1-AP (S1-Application Protocol). In LTE, a protocol stack of the S1-U interface is divided into the following protocol layers from bottom to top: L1 protocol, L2 protocol, UDP/IP (User Data Protocol/Internet Protocol), and GTP-U (GPRS Tunneling Protocol-User plane).
At present, due to the lack of frequency spectrum resources and the sharp increase of high-traffic services of mobile users, in order to increase user throughput and improve mobility performance, the demand of performing hotspot coverage by adopting high-frequency points such as 3.5 GHz is increasingly obvious, and adopting low-power nodes becomes a new application scenario. However, since signal attenuation of high-frequency points is comparatively serious, the coverage range of new cells is comparatively small and the new cells and the existing cells are not at the same site, hence, if users move between these new cells or between the new cells and the existing cells, frequent handover processes inevitably will be caused, consequently user information will be frequently transmitted between the base stations, a very great signaling shock will be caused to a core network and the introduction of numerous small cellular base stations on a wireless side will be restrained. FIG. 2 is a schematic diagram of an overall architecture of a small cellular base station system. As shown in FIG. 2, the architecture comprises an MME, an SGW, UE(s) and base stations (eNobeB, called as eNB for short), herein interfaces between the UE and the eNB are Uu interfaces, an interface between the MeNB and the MME is an S1-MME (S1 for the control plane) interface, an interface between the M-eNB or SeNB and the SGW is an S1-U interface, and an interface between the eNBs is Xn interface. User data can be issued from the core network to users through the M-eNB, and can also be issued from the core network to the users through the S-eNB. After the users access to the M-eNB, a dual-connection can be implemented by adding, modifying and deleting the S-eNB.
Simultaneously, with wide demands by users for local services and Internet services, for the UEs and the core network, a permanent online function is supported, i.e., after a data connection is established, the UE can transmit data to external data networks at any time, the external data networks can also transmit data to the UE. The external data networks involved in this document refer to IP networks which do not belong to a PLMN (Public Land Mobile Network) but are connected with the PLMN, and for example, can be home internal networks or Internet. This function is called as an LIPA@LN (Local IP Access at Local Network) or SIPTO@LN (Selected IP Traffic Offload at Local Network) function. If an L-GW (Local Gateway) which supports LIPA or SIPTO services is arranged on a base station (which can be a macro eNB and can also be a home eNB), this base station is called as a collocated L-GW. For a system architecture supporting SIPTO@LN and collocated L-GW, see FIG. 3.
Under the current LTE system, in order to realize an SIPTO@LN function, in a scenario of a collocated L-GW, a base station (which can be a macro base station and can also be a home base station) on which the collocated L-GW is located does not support mobility of an SIPTO@LN service, i.e., when the UE moves to another base station, an SIPTO@LN PDN (Public Data Network) connection needs to be released. A related release manner is that, after UE handover is successfully completed, the release is triggered through a UE text release message of an S1 or X2 interface. If what is performed by the UE is an S1 handover process, the base station receives the UE text release message on the S1 interface and a cause value indicates handover success, the base station notifies the L-GW through an internal channel to perform SIPTO@LN connection release. If what is performed by the UE is an X2 handover process, after the source base station receives the UE text release message on the X2 interface, the source base station notifies the L-GW through an internal channel to perform SIPTO@LN connection release. Under the above-mentioned small base station system, since concepts of MeNB (Master eNB) and SeNB (Secondary eNB) are introduced, a specific position of the collocated L-GW and how to implement SIPTO@LN connection release when the MeNB or SeNB changes are not considered in the related art.